Treatment and diagnostic catheters with hydrogel electrodes

ABSTRACT

Straight and curved catheters for treatment or diagnoses of tissue, including cardiac tissue, using hydrogel virtual electrodes and hydrogel sensing electrodes are disclosed. Each catheter comprises at least one conductive hydrogel electrode, whether a virtual electrode or a sensing electrode. Hydrogel virtual electrodes may be used to deliver ablative energy or chemotherapeutic agents to tissue. Hydrogel sensing electrodes may be used to map various electrical activity of tissue. The ablation catheters include a variety of hydrogel delivery features to deliver the conductive hydrogel electrodes against or adjacent to tissue to be treated. Each hydrogel delivery feature comprises at least one opening in the distal portion of the catheter and may also include a permeable or semi-permeable membrane. The mapping catheters include conductive hydrogel disks (i.e., conductive hydrogel sensing electrodes) and nonconductive hydrogel disks. Methods of treating and diagnosing tissue using hydrogel virtual electrodes and hydrogel sensing electrodes are also disclosed.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention is directed toward hydrogel electrode cathetersfor treatment and diagnosis of tissue. More specifically, the instantinvention relates to treatment and diagnostic catheters with hydrogelvirtual and sensing electrodes.

b. Background Art

Catheters have been in use for medical procedures for many years.Catheters can be used for medical procedures to examine, diagnose, andtreat tissue while positioned at a specific location within the bodythat is otherwise inaccessible without more invasive procedures (e.g.,medical procedures involving the human heart). During these procedures acatheter is inserted into a vessel located near the surface of a humanbody (e.g., an artery or vein in the leg, neck, or arm of the patient)and is guided or threaded through the vessels, sometimes with the aid ofa guidewire or introducer, to a specific location within the body forexamination, diagnosis, and treatment. For example, one procedure oftenreferred to as “ablation” utilizes a catheter to convey energy (e.g.,electrical or thermal) or a chemical to a selected location within thehuman body to create necrosis, which cuts off the path for stray orimproper electrical signals. Another procedure often referred to as“mapping” utilizes a catheter with one or more sensing electrodes tomonitor various forms of electrical activity in the human body.

It is well known that benefits may be gained by forming lesions intissue during catheter ablation if the depth and location of the lesionsbeing formed can be controlled. In particular, it can be desirable toelevate tissue temperature to around 50° C. until lesions are formed viacoagulation necrosis, which changes the electrical properties of thetissue. When sufficiently deep lesions are formed at specific locationsin cardiac tissue via coagulation necrosis, undesirable atrialfibrillations may be lessened or eliminated. “Sufficiently deep” lesionsmeans transmural lesions in some cardiac applications.

Several difficulties may be encountered, however, when attempting toform adequately-deep lesions at specific locations using some existingablation electrodes. For example, when forming lesions withradiofrequency (RF) energy, high temperature gradients are oftenencountered in the vicinity of the electrode. At the edges of someexisting electrodes are regions of very high current density, leading tolarge temperature gradients and hot spots. These “edge effects” mayresult in the formation of undesirable coagulum and charring of thesurface tissue. For example, undesirable coagulum may begin to form whenblood reaches around 80° C. for an appreciable length of time, andundesirable tissue charring and desiccation may be seen when tissuereaches around 100° C. for an appreciable length of time. There are twomain types of undesirable coagulum: coagulum that adheres to and damagesthe medical device; and coagulum blood clots or curds that may enter apatient's bloodstream, possibly resulting in other health problems forthe patient. Charring of the surface tissue may also have deleteriouseffects on a patient.

During RF ablation, as the temperature of the electrode is increased,the contact time required to form an adequately-deep lesion decreases,but the likelihood of charring surface tissue and forming undesirablecoagulum increases. As the temperature of the electrode is decreased,the contact time required to form an adequately-deep lesion increases,but the likelihood of charring surface tissue and forming undesirablecoagulum decreases. It is, therefore, a balancing act trying to ensurethat tissue temperatures are adequately high for long enough to createdeep lesions, while still preventing or minimizing coagulum formationand/or charring of the surface tissue. Active temperature control mayhelp, but the placement of thermocouples, for example, is tricky andsetting the RF generator for a certain temperature becomes an empiricalexercise as actual tissue temperatures are generally different fromthose recorded next to the electrode due to factors such as convectionand catheter design.

Conventional mapping catheters may include, for example, a plurality ofadjacent ring electrodes constructed from platinum or some other metal.Since mapping catheters are desirably disposable, incorporation ofrelatively expensive platinum electrodes may be disadvantageous.

Another difficulty encountered with existing ablation catheters andmapping catheters is how to ensure adequate tissue contact. For example,current techniques for creating linear lesions (the term “linear lesion”as used herein means an elongated, continuous or uninterrupted lesion,whether straight or curved and whether comprising a single line ofablation or a series of connected points or lines of ablation forming atrack, that blocks electrical conduction) in endocardial applicationsmay include dragging a conventional catheter on the tissue, using anarray electrode, or using pre-formed electrodes. All of these devicescomprise rigid electrodes that do not always conform to the tissuesurface, especially when sharp gradients and undulations are present,such as at the ostium of the pulmonary vein in the left atrium and theisthmus of the right atrium. Consequently, continuous linear lesions aredifficult to achieve. Whether forming lesions or mapping in a heart, thebeating of the heart, especially if erratic or irregular, furthercomplicates matters, making it difficult to keep adequate contactbetween electrodes and tissue for a sufficient length of time. Forexample, with a rigid electrode, it can be quite difficult to maintainsufficient contact pressure during lesion formation until an adequatelesion has been formed. These problems are exacerbated on contoured ortrabeculated surfaces. If the contact between electrodes and tissuecannot be properly maintained, quality lesions or accurate mapping areunlikely to result.

Catheters based upon a virtual electrode that deliver RF energy viaconductive fluid flowing into the patient's body address some of thedifficulties with ablation catheters, but these ablation catheters oftenrequire high flow rates of the conductive fluid (e.g., typically around70 milliliters per minute) to maintain effective cooling for high-powerRF applications. The introduction of a large amount of conductive fluidinto a patient's bloodstream may have detrimental effects on thepatient.

Thus, there remains a need for ablation catheters and mapping cathetersthat address these issues with the existing designs.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the disclosed invention to provideimproved treatment and diagnostic catheters.

In one form, the present invention comprises a catheter for treatment oftissue, the catheter comprising at least one conductive hydrogel virtualelectrode adapted to contact the tissue to be treated. In this form, thecatheter includes a distal portion that comprises a straight section; ahoop-shaped section; an offset that joins the straight section to thehoop-shaped section; an active region along the hoop-shaped section; anda hydrogel delivery feature along the active region, wherein thehydrogel delivery feature is adapted to be placed against the tissue tobe treated. The hoop-shaped section may define a distally-facingsurface, and the hydrogel delivery feature may be on thatdistally-facing surface. Alternatively, the hoop-shaped section maydefine a radially outer peripheral wall that includes anoutwardly-facing surface, and the hydrogel delivery feature may be onthat outwardly-facing surface. The hydrogel delivery feature comprisesat least one opening extending through the distally-facing surface orthe outwardly-facing surface. The at least one opening may comprise, forexample, a single row of hydrogel portholes, a plurality of rows ofhydrogel portholes radially, a single hydrogel slot, or a plurality ofhydrogel slots. The at least one opening my be centered about a radialapex of the distally-facing surface or of the outwardly-facing surface.

In another form, the present invention again comprises a catheter fortreatment of tissue, the catheter comprising at least one conductivehydrogel virtual electrode adapted to contact the tissue to be treated.In this form, the catheter includes a distal portion that comprises astraight active region, the straight active region extending parallel toa catheter longitudinal axis; and a hydrogel delivery feature along thestraight active region, the hydrogel delivery feature being adapted tobe placed against the tissue to be treated. The straight active regiondefines an outer peripheral wall, wherein the outer peripheral walldefines an outwardly-facing surface, wherein the hydrogel deliveryfeature is on the outwardly-facing surface. The hydrogel deliveryfeature comprises at least one opening extending through the outerperipheral wall and its outwardly-facing surface. The at least oneopening may comprise, for example, a single row of hydrogel portholes, aplurality of rows of hydrogel portholes radially, a single hydrogelslot, or a plurality of hydrogel slots. The at least one opening may becentered about a radial apex of the outwardly-facing surface.

In yet another form, the present invention comprises a catheter fortreatment of tissue, the catheter comprising at least one conductivehydrogel virtual electrode, wherein the at least one conductive hydrogelvirtual electrode is contained within a permeable or semi-permeablecontainment membrane adapted to contact the tissue to be treated. Themembrane may comprise a shaped membrane adapted to take a predeterminedconfiguration when filled with conductive hydrogel. For example, thecontainment membrane, when filled with conductive hydrogel, may beadapted to form a protuberance having a conformable surface to contactthe tissue to be treated. This protuberance may take the shape of ahemisphere, a knob, a flattened gob, a hook, or a hoop.

In another form, the present invention comprises a drug deliverycatheter for treatment of cardiac arrhythmias. In this embodiment, thecatheter comprising a distal portion having an active region; a lumenextending inside the catheter adjacent to the active region; and ahydrogel delivery feature along the active region and in fluidcommunication with the lumen, wherein the hydrogel delivery feature isadapted to be placed against arrhythmia-producing, cardiac tissue insideof a heart. A conductive hydrogel matrix is present in the lumen,wherein the conductive hydrogel matrix is loaded with, for example, awater-soluble and ionic dispensable drug formulation. The hydrogeldelivery feature may comprise, for example, a plurality of hydrogelportholes; and a permeable membrane attached at the plurality ofhydrogel portholes and adapted to be alternatingly extendable out of andretractable back into the plurality of hydrogel portholes, wherein themembrane is adapted to contain the conductive hydrogel matrix, whereinthe membrane is adapted to make contact with the cardiac tissue, andwherein the membrane is adapted to be traversable by the drugformulation.

In still another form, the present invention comprises a drug deliverysystem for treatment of cardiac arrhythmias. The system comprises acatheter having a distal portion. The distal portion of the cathetercomprises an active region; a lumen extending adjacent to the activeregion, the lumen being adapted to contain a conductive hydrogel matrixloaded with, for example, a water-soluble and ionic dispensable drugformulation; and a hydrogel delivery feature. The hydrogel deliveryfeature comprises an opening through the active region, the openingbeing in fluid communication with the lumen and being adapted to beplaced against arrhythmia-producing, cardiac tissue; and a permeablemembrane attached at the opening and adapted to be alternatinglyextendable out of and retractable back into the opening, wherein themembrane is adapted to contain the conductive hydrogel matrix, whereinthe membrane is adapted to make contact with the cardiac tissue, andwherein the membrane is adapted to be traversable by the ionicdispensable drug formulation. In this embodiment, the system alsocomprises a current supply adapted to deliver low-intensity directcurrent to the conductive hydrogel matrix. The opening through thesidewall of the catheter may comprise, for example, at least onehydrogel porthole or at least one hydrogel slot.

In another form, the present invention comprises a diagnostic catheterfor diagnosing cardiac tissue, the catheter comprising at least oneconductive hydrogel sensing electrode. The at least one conductivehydrogel sensing electrode may comprise a plurality of isolated,conductive hydrogel disks that are electrically separated bynonconductive hydrogel disks. These conductive and nonconductivehydrogel disks may be constructed from, for example, high-viscosity,rigid hydrogel that is substantially unaffected by moisture. Theconductive hydrogel disks may be adhered to the nonconductive hydrogeldisks. In this embodiment, each of the plurality of conductive hydrogeldisks is electrically connected with a separate electrical lead (e.g., asilver or silver-chloride coated wire) for transmitting electricalsignals from the treatment site to instrumentation outside of apatient's body.

In yet another form, the present invention comprises a method oftreating cardiac tissue. The method comprises the steps of guiding anablation catheter having at least one conductive hydrogel virtualelectrode to the cardiac tissue to be treated; introducing the at leastone conductive hydrogel virtual electrode against the cardiac tissue;and directing ablative energy to the cardiac tissue via the at least oneconductive hydrogel virtual electrode.

In still another form, the present invention comprises a method oftreating cardiac tissue, the method comprising the steps of filling atleast a distal portion of a catheter lumen with conductive hydrogel, thecatheter lumen extending adjacent to a catheter active region on acatheter outer surface; guiding the catheter active region into contactwith the cardiac tissue to be treated; activating a hydrogeldisplacement device to advance the conductive hydrogel toward the activeregion until the conductive hydrogel broaches the catheter outer surfaceto thereby introduce at least one conductive hydrogel virtual electrodeagainst the cardiac tissue; directing ablative energy through the atleast one conductive hydrogel virtual electrode and into the cardiactissue; and activating the hydrogel displacement device to retract theconductive hydrogel and thus the at least one conductive hydrogelvirtual electrode from contact with the cardiac tissue and back into thecatheter lumen.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is fragmentary, isometric view of the distal portion of anablation catheter according to a first embodiment of the presentinvention adjacent to the ostium of a pulmonary vein.

FIG. 2 is a fragmentary, isometric view of the distal portion of anablation catheter according to a second embodiment of the presentinvention.

FIG. 3 is a fragmentary, isometric view of the distal portion of anablation catheter according to a third embodiment of the presentinvention depicted next to the ostium of a pulmonary vein.

FIG. 4 is a fragmentary, isometric view of the distal portion of anablation catheter according to a fourth embodiment of the presentinvention.

FIG. 5 is a fragmentary, top view of the distal portion of an ablationcatheter according to a fifth embodiment of the present invention.

FIG. 6 is a fragmentary, end view (looking distally) of the ablationcatheter depicted in FIG. 5, shown with at least partially deployedconductive hydrogel protruding from the hydrogel portholes.

FIG. 7 is a fragmentary, side view of the ablation catheter depicted inFIGS. 5 and 6, shown with the conductive hydrogel retracted into thecatheter.

FIG. 8 is a fragmentary, top view of the distal portion of an ablationcatheter according to a sixth embodiment of the present invention.

FIG. 9 is a fragmentary, top view of the distal portion of an ablationcatheter according to a seventh embodiment of the present invention.

FIG. 10 is a fragmentary, top view of the distal portion of an ablationcatheter according to an eighth embodiment of the present invention.

FIG. 11 is an enlarged, fragmentary view of the portion that is circledin FIG. 10.

FIG. 12 is a fragmentary, cross-sectional view taken along line 12-12 ofFIG. 10, shown with the conductive hydrogel poised at the hydrogelporthole exits prior to being forced to protrude from the portholes.

FIG. 13 is similar to FIG. 12, but depicts the conductive hydrogel inits deployed configuration, protruding from the portholes against thetissue to be treated.

FIG. 14 is a fragmentary, cross-sectional view taken along line 14-14 ofFIG. 13 and depicts ablative energy being transferred to the tissuethrough the conductive hydrogel.

FIG. 15 is a fragmentary, cross-sectional view of the distal portion ofan ablation catheter according to a ninth embodiment and depicts amembrane containing the protruding conductive hydrogel.

FIG. 16 is a fragmentary, top view of the distal portion of an ablationcatheter according to a tenth embodiment of the present invention priorto deployment of the conductive hydrogel.

FIGS. 17, 18, and 19 are fragmentary, top views of the distal portion ofan ablation catheter according to a first variant, a second variant, anda third variant, respectively, of the tenth embodiment of the presentinvention.

FIG. 20 is a fragmentary, cross-sectional view of the distal portion ofa hydrogel drug delivery catheter according to an eleventh embodiment ofthe present invention.

FIG. 21 is a fragmentary, cross-sectional view of the distal portion ofa hydrogel drug delivery catheter according to a twelfth embodiment ofthe present invention.

FIG. 22 is a fragmentary, top view of the distal portion of a diagnosticcatheter according to a thirteenth embodiment of the present invention.

FIG. 23 is a fragmentary, cross-sectional view taken along line 23-23 ofFIG. 22.

FIG. 24 is a fragmentary, end view (looking distally) of the distalportion of a diagnostic catheter according to a fourteenth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a variety of catheters with hydrogelvirtual electrodes for treatment and diagnosis of tissue (e.g., humancardiac tissue). In particular, FIGS. 1-19 depict a number of differentconfigurations for hydrogel virtual electrode ablation catheters, FIGS.20 and 21 depict hydrogel drug delivery catheters, and FIGS. 22-24depict hydrogel diagnostic catheters. Whenever there may be contactbetween the hydrogel and a patient's blood, each of the cathetersdepicted in FIGS. 1-24 uses hemocompatible hydrogel that may or may notbe radiopaque. Viscoelastic hydrogel, for example, may be used in thetreatment catheters depicted in FIGS. 1-21; and a high-viscosity, rigidhydrogel that is substantially unaffected by moisture (e.g., a hydrogelthat does not swell in the presence of moisture) may be used in thediagnostic catheters depicted in FIGS. 22-24. In all of the embodimentsdepicted and described herein, the hydrogel does not enter a patient'sbloodstream in any appreciable amounts. The portholes, slots, andopenings depicted in FIGS. 1-21 are adapted to allow the hydrogel to bealternatingly forced from and retracted back into the catheter using ahydrogel displacement device such as a plunger, a pump, or a syringe,none of which are shown in the drawings. For example, a screw-, gear-,or piston-pump may be used to move the hydrogel under whatever pressureis required (e.g., 500 psi).

FIG. 1 is a fragmentary, isometric view of the distal portion 101 of anablation catheter according to a first embodiment of the presentinvention. In this embodiment, the distal portion 10′ of the ablationcatheter comprises a straight section 12 and a curved or hoop-shapedsection 14 that are joined at a bend or offset 16. A longitudinal axis18 extends through both the straight section 12 and the curved section14. As used herein, the term “longitudinal axis” refers to thelongitudinal axis extending through the straight section 12 and throughthe curved section 14 of the ablation catheter, from the proximal end(not shown) of the catheter to the distal end 20 of the ablationcatheter. The curved or hoop-shaped section 14 is C-shaped as shown, butmay define a completely circular configuration rather than the open,C-shape depicted in FIG. 1. The bend or offset 16 may be formed orconfigured as shown in FIG. 1, wherein the offset displaces the straightsection 12 of the catheter to the side, causing the straight section 12to meet the curved section 14 of the catheter along the perimeter of thehoop-shaped curved section 14 (i.e., substantially perpendicularly tothe plane containing the C-shaped curved section 14 and along theimaginary cylindrical surface formed by sliding the C-shaped curvedsection parallel to the longitudinal axis 18 of the straight section 20to create a substantially cylindrical surface). Alternatively, theoffset 78 (e.g., Fogs. 5-7) may be configured so that the straightsection 84 approaches the plane containing the C-shaped or hoop-shapedcurved section 78 near the center of the “C” or hoop (see, e.g., FIG.6). The “straight section” 84 of the catheter shaft is “straight”relative to the C-shaped or hoop-shaped section 78, but remains flexibleenough to be navigated through a patient's vasculature to a treatmentsite (e.g., the ostium 22 of a pulmonary vein 24 as shown in FIG. 1).

The curved section 14 of the ablation catheter defines a distally-facingsurface 26. As shown in FIG. 1, the distally-facing surface 26 is placedagainst the tissue 28 to be treated (e.g., the ostium 22 of a pulmonaryvein 24 as shown in FIG. 1). In the embodiment depicted in FIG. 1, thedistally-facing surface 26 defines a distally-facing radial apex 30. Thedistally-facing radial apex is the most distal surface of the curvedsection 14 of the ablation catheter. In FIG. 1, the distally-facingradial apex 30 defines a C-shaped line which, in the embodiment depictedin FIG. 1, overlies a porthole centerline 32 for a plurality ofdistally-facing hydrogel portholes 34. In particular, the ablationcatheter depicted in FIG. 1 includes a hydrogel deployment featurecomprising a single row of hydrogel portholes 34 centered along theporthole centerline 32 on the radial apex 30 of the distally-facingsurface 26. In the configuration depicted in FIG. 1, the conductivehydrogel used to treat the tissue remains inside the distal portion 101of the ablation catheter and has not yet been forced to protrude throughthe hydrogel portholes 34 into contact with the tissue 28 to be treated.As shown in FIG. 1, the ablation catheter may also include a rounded tip36, which may or may not be conductive.

FIG. 2 is a fragmentary, isometric view of the distal portion 10 ^(II)of an ablation catheter according to a second embodiment of the presentinvention. Similar to the embodiment 10 ^(I) depicted in FIG. 1, theablation catheter depicted in FIG. 2 comprises a straight section 12 anda curved section 38 joined by a bend or offset 16. In the embodiment 10^(II) depicted in FIG. 2, the hydrogel deployment feature comprisesconcentric arcs of staggered hydrogel portholes, including a firstplurality of hydrogel portholes 40 along an outer arc and a secondplurality of hydrogel portholes 42 along an inner arc. Thus, in theembodiment depicted in FIG. 2, the hydrogel deployment feature is againon the distally-facing surface 44 of the distal portion 10 ^(II) of theablation catheter. In the configuration depicted in FIG. 2, theconductive hydrogel 46 has been pushed distally in the catheter until itis flush with the outer surface of the curved section where eachhydrogel porthole 40,42 broaches the outer surface of the catheter.Thus, the conductive hydrogel 46, if forced distally any further, willprotrude from the hydrogel portholes 40,42, distally away from thedistally-facing surface 44 of the ablation catheter, as discussedfurther below.

The concentric arcs of staggered hydrogel portholes comprise a pluralityof hydrogel portholes on alternating sides of a porthole centerline 48,thereby forming a zigzagging row of hydrogel portholes 40,42. Ingeneral, the hydrogel porthole configuration depicted in FIG. 2 may beused to make a wider arcuate, linear lesion than the lesion that may beformed by the single row of hydrogel portholes 34 depicted in FIG. 1without greatly changing the size of each individual porthole. Bystaggering the portholes 40 of the outer arc of hydrogel portholesrelative to the portholes 42 of the inner arc of hydrogel portholes, itis possible to reduce opportunities for gaps to exist in the lesionformed during treatment. Lesion formation is discussed further below.

FIG. 3 is a fragmentary, isometric view of the distal portion 10 ^(III)of an ablation catheter according to a third embodiment of the presentinvention. Similar to what is depicted in FIG. 1, FIG. 3 depicts thedistally-facing surface 50 of the distal portion 10 ^(III) of theablation catheter at the ostium 22 of a pulmonary vein 24. In thisembodiment, the distal portion 10 ^(II) of the ablation catheter againincludes a straight section 12 and a curved section 52 joined by a bendor offset 16. Similar to the embodiments depicted in FIGS. 1 and 2, theembodiment of FIG. 3 also comprises a hydrogel deployment feature on thedistally-facing surface 50 of the curved section 52 of the catheter. Inthe third embodiment, the hydrogel portholes 34, 40, 42 of FIGS. 1 and 2have been replaced by a longitudinally-extending hydrogel slot 54 thatstraddles a slot centerline 56 on the radial apex of the distally-facingsurface 50. Again, as was shown in FIG. 2, in the configuration depictedin FIG. 3, the conductive hydrogel 46 fills the longitudinally-extendinghydrogel slot 54, flush with the distally-facing surface 50 of theablation catheter, but does not yet protrude outwardly through thehydrogel slot 54. If the tissue 28 to be treated has a relatively flatsurface, ablative energy may be applied to the tissue while theconductive hydrogel 46 is in this flush, non-protruding configuration.As discussed further below, however, if the tissue 28 to be ablatedcomprises trabeculations or undulations, the column or segment ofconductive hydrogel in the catheter may be forced distally until theconductive hydrogel 46 actually protrudes from thelongitudinally-extending hydrogel slot 54 so that the conductivehydrogel 46 has an opportunity to conform to the trabeculated tissuesurface (see, e.g., FIGS. 13 and 14).

FIG. 4 is a fragmentary, isometric view of the distal portion 10 ^(IV)of an ablation catheter according to a fourth embodiment of the presentinvention. The embodiment depicted in FIG. 4 is similar to theembodiments depicted in FIGS. 1-3, except for the hydrogel deploymentfeature. In FIG. 4, the conductive hydrogel 46 is deployed or deliveredthrough the catheter and against the tissue 28 being ablated via aplurality of laterally-extending or transversely-extending hydrogelslots 58. These laterally-extending hydrogel slots 58 extendsubstantially perpendicularly to the arc or line defining a slotcenterline 60 along the radial apex of the distally-facing surface 62 ofthe curved section 64 of the ablation catheter. The transverse length 66of each hydrogel slot 58 may be adjusted to obtain the desired lesionwidth. The longitudinal width 68 of each hydrogel slot 58 as well as theseparation distance 70 between adjacent slots may be adjusted to controlpotential gaps in the arcuate lesion formed during use of the ablationcatheter depicted in FIG. 4. Similar to what is depicted in FIGS. 2 and3, the conductive hydrogel 46 depicted in FIG. 4 has been advanceddistally until the hydrogel 46 is flush with the distally-facing surface62 of the ablation catheter where the laterally-extending hydrogel slots58 pierce or broach the outer surface of the curved section 64 of theablation catheter.

FIGS. 5-7 are fragmentary views of the distal portion 10 ^(V) of anablation catheter according to a fifth embodiment of the presentinvention. In the embodiment depicted in FIGS. 5-7, the hydrogeldeployment feature comprises a plurality of hydrogel portholes 72arranged along a single row, similar to the plurality of portholes 34depicted in FIG. 1. In the embodiment of FIGS. 5-7, however, the singlerow of hydrogel portholes 72 is present along a porthole centerline 74on the radial apex of an outer peripheral wall 76 of the curved section78 rather than being on the radial apex 30 of the distally-facingsurface 26 as shown in FIG. 1. In other words, the ablation catheterdepicted in FIGS. 5-7 comprises an inner peripheral wall 80 and an outerperipheral wall 76 on the hoop-shaped or curved section 78, and theportholes 72 extend substantially radially through the outer peripheralwall 76 of this C-shaped or hoop-shaped curved section 78 of theablation catheter.

FIG. 6 is a fragmentary, end view (looking distally) at the distalportion 10 ^(V) of the ablation catheter depicted in FIG. 5, shown withat least partially deployed conductive hydrogel 46 protruding from thehydrogel portholes 72; and FIG. 7 is a fragmentary, side view of theablation catheter depicted in FIGS. 5 and 6, shown with the conductivehydrogel 46 retracted into the catheter. As depicted to best advantagein FIGS. 6 and 7, this fifth embodiment of the ablation catheter alsoincludes an offset 82 that is slightly different from the offset 16depicted in FIGS. 1-4. In particular, the offset 82 depicted in FIGS.5-7 places the straight section 84 of the catheter shaft so that, ifextended distally, the distal end of the straight section 84 would passthrough a plane containing the C-shaped or hoop-shaped curved section 78of the distal portion 10 ^(V) of the ablation catheter at nearly thecenter of the C-shaped or hoop-shaped curved section 78. Since thehydrogel portholes 72 of this embodiment pass through the outerperipheral wall 76, this version of the ablation catheter may beinserted inside of a pulmonary vein 24, for example, rather than beingplaced at the ostium 22 of a pulmonary vein 24 as depicted in FIGS. 1and 3. Since this version 10 ^(V) of the ablation catheter may be placedinside of a pulmonary vein 24, configuring the offset 82 to displace thestraight section 84 toward the center of the C-shaped curved section 78results in a configuration that places the straight section 84 of thecatheter shaft away from the wall of, for example, a pulmonary vein 24into which the ablation catheter has been inserted to treat tissue 28.

In FIG. 5, the conductive hydrogel is undeployed. In FIG. 6, on theother hand, the conductive hydrogel 46 has been at least partiallydeployed and protrudes from each of the hydrogel portholes 72. Ablativeenergy (e.g., RF energy) may be applied to the hydrogel 46 in its atleast partially deployed configuration depicted in FIG. 6. If desired,additional hydrogel may be deployed from the hydrogel portholes 72 untilthe protruding portions of hydrogel 46 touch any adjacent protrudingportions of hydrogel 46 thereby eliminating gaps 86. By thus controllingthe amount of conductive hydrogel 46 protruding from the hydrogelportholes 72, it is possible to control potential gaps in a linearlesion formed by the ablative energy passing through the protrudingconductive hydrogel 46. As shown in FIG. 6, the conductive hydrogel 46itself may come into contact with the tissue 28 (see, e.g., FIGS. 1 and3) to be treated. Alternatively, as described below in connection with,for example, FIG. 15, the conductive hydrogel 46, in all of theembodiments, may be contained within a permeable or semi-permeablecontainment bag or liner or membrane 88. In these latter configurations,the containment membrane 88 makes the actual contact with the tissue 28to be treated rather than the conductive hydrogel 46 itself.

FIG. 8 is a fragmentary, top view of the distal portion 10 ^(VI) of anablation catheter according to a sixth embodiment of the presentinvention. This embodiment is similar to the embodiment depicted inFIGS. 5-7, but the plurality of hydrogel portholes 72 have been replacedwith a longitudinally-extending hydrogel slot 90 as the hydrogeldeployment feature. This longitudinally-extending hydrogel slot 90straddles a slot centerline 92 along the radial apex of the outerperipheral wall 94 of the curved section 96 of the distal portion 10^(VI) of the ablation catheter. The longitudinally-extending hydrogelslot 90 is present between a distal slot edge 98 and a proximal slotedge 100. The longitudinally-extending hydrogel slot 90 depicted in FIG.8 is similar to the longitudinally-extending hydrogel slot 54 depictedin FIG. 3; however, the slot 90 depicted in FIG. 8 extends through theouter peripheral wall 94 of the curved section 96 rather than throughthe distally-facing surface 50 of the curved section 52 (FIG. 3). Thus,the ablation catheter depicted in FIG. 8 is again configured for useinside, for example, a pulmonary vein 24 so that the conductive hydrogel46 extending into or through the longitudinally-extending hydrogel slot90 would come into contact with the tissue 28 to be treated. With thistype of target use, the ablation catheter depicted in FIG. 8 may againcomprise an offset 82 that places the straight section 84 of thecatheter shaft central to the curved, C-shaped or hoop-shaped section 96as discussed in connection with FIGS. 5-7.

FIG. 9 is a fragmentary, top view of the distal portion 10 ^(VII) of anablation catheter according to a seventh embodiment of the presentinvention. In this embodiment, the hydrogel 46 is delivered adjacent toor against the tissue 28 to be ablated via a hydrogel deployment featurecomprising a first plurality of hydrogel portholes 102 arranged in adistal arc and a second plurality of hydrogel portholes 104 arranged ina proximal arc. These arcs of portholes symmetrically straddle aporthole centerline 106 along the radial apex of the outer peripheralwall 108 of the curved section 110 of the distal portion 10 ^(VII) ofthe ablation catheter, and, in the specific configuration depicted inFIG. 9, each hydrogel porthole 102 of the distal arc has a correspondinghydrogel porthole 104 along the proximal arc. These two arcs ofportholes could be offset or staggered, similar to what is shown in FIG.2. In the embodiment of FIG. 9, however, the portholes 102, 104 extendthrough the outer peripheral wall 108 of the curved section 110 of thedistal portion 10 ^(VII) of the ablation catheter rather than throughthe distally-facing surface 44 of the distal portion 10 ^(II) of theablation catheter as shown in FIG. 2. Also, more than two arcs ofhydrogel portholes may be present. For example, a third, intermediatearc of hydrogel portholes (not shown) may be present between thehydrogel portholes 102 of the distal arc and the hydrogel portholes 104of the proximal arc depicted in FIG. 9.

FIG. 10 is a fragmentary, top view of the distal portion 10 ^(VIII) ofan ablation catheter according to an eighth embodiment of the presentinvention. The embodiment 10 ^(VIII) depicted in FIG. 10 is similar tothe fifth embodiment 10 ^(V) depicted in FIGS. 5-7. In FIG. 10, however,the portion of the catheter comprising the hydrogel deployment feature(i.e., the plurality of hydrogel portholes along the active region 112of the catheter) is relatively straight and not C-shaped or hoop-shaped.The plurality of hydrogel portholes includes a most distal porthole 114,a most proximal porthole 116, and at least one intermediate porthole 118arranged along a porthole centerline 120. These portholes 114, 116, 118extend through an outer peripheral wall 122 of the distal portion 10^(VIII) of the ablation catheter, substantially perpendicularly to thelongitudinal axis 124 of the catheter.

FIG. 11 is an enlarged, fragmentary view of the portion that is circledby a dashed line in FIG. 10. As shown in FIG. 11, a bridge 126 ispresent between adjacent portholes (e.g., 114, 118, in FIG. 11). Thewidth of the bridge is the distance between a distal trailing edge 128of one porthole 118 and the proximal leading edge 130 of an adjacentporthole 114. Adjusting the distance 132 between adjacent portholesclearly affects the size of the bridge 126 between portholes. Byadjusting the size of the bridges 126 and the size of the portholes 114,116, 118 themselves, it is possible to attain a configuration for theablation catheter to produce a linear lesion of a predetermined depthand length, and a lesion with or without gaps in it. Similar adjustmentscould be made to the hydrogel portholes depicted in any of the otherfigures.

FIG. 12 is a fragmentary, cross-sectional view taken along line 12-12 ofFIG. 10. Visible for the first time in this figure is one possiblecross-sectional configuration for the catheter shaft for all of theembodiments. In this configuration, the catheter shaft includes a firstlumen 134 through which the conductive hydrogel 46 moves and a secondlumen 136 containing a shape memory wire or a steering wire 138 used toposition the hydrogel 46 deployment feature adjacent to the tissue 28 tobe treated. In FIG. 12, the conductive hydrogel 46 is poised fordeployment. In other words, the hydrogel 46 has been pushed distally inthe catheter until the conductive hydrogel 46 is flush with the outersurface 122 of the ablation catheter. The conductive hydrogel remainswithin the hydrogel portholes 114, 116, 118, but may be placed adjacentto the tissue to be treated. Thus, as mentioned above, with the hydrogelthereby poised for deployment, if the active region 112 (FIG. 10) of theablation catheter (i.e., the hydrogel portholes in the depictedembodiment) were placed against tissue to be treated, and if that tissuecomprised a relatively flat surface, ablative energy may be transmittedto the tissue with the conductive hydrogel positioned as shown in FIG.12. As previously mentioned, the rounded tip 36 of the catheter may ormay not be conductive. If the rounded tip is nonconductive, it maycomprise, for example, a sphere or “plug” of adhesive or polymer 140that seals the end of the catheter lumen.

FIG. 13 is similar to FIG. 12, but depicts the conductive hydrogel 46 inits deployed configuration, protruding from the hydrogel portholes 114,116, 118 against the tissue 28 to be treated. In order to facilitatebetter contact with the tissue 28 to be ablated, particularly when thesurface 142 of the tissue 28 is trabeculated or undulated as shown inFIG. 13, and to help eliminate potential gaps in the lesion that isformed by the ablative energy delivered through the conductive hydrogel46, the conductive hydrogel may be forced distally through the firstlumen 134 (i.e., in the direction of arrow 144 in FIG. 13) of thecatheter shaft until the portions of hydrogel protruding through eachhydrogel porthole contact 114, 116, 118 adjacent portions of hydrogel asshown in FIG. 13. In the embodiment depicted in this figure, nocontainment bag or membrane or liner 88 is present (compare what isshown in FIG. 15, which includes a membrane 88); and the conductivehydrogel 46 itself directly contacts the tissue 28 being treated. Again,as previously mentioned, after the tissue treatment has been completed,the conductive hydrogel 46 is pulled or pumped back into the shaft ofthe ablation catheter (i.e., in the direction of arrow 146 in FIG. 13)before the catheter is extracted from the patient. Thus, very little, ifany, conductive hydrogel 46 remains in the patient's body after thetreatment is completed.

FIG. 14 is a fragmentary, cross-sectional view taken along line 14-14 ofFIG. 13 and depicts ablative energy 148 being transferred to the tissue28 through the conductive hydrogel 46. This figure depicts additionaldetails about one possible configuration for the catheter shaft. In thisdepicted configuration, the first lumen 134, through which theconductive hydrogel 46 is moved, comprises a nearly-circular subportion150 and a rounded-rectangular subportion 152. The rounded-rectangularsubportion 152 may be used to retain an electrode 154 that deliversablative energy 148 (e.g., RF energy) through the conductive hydrogel 46to the tissue 28 being treated. The second lumen 136, when present, maycontain the shape memory wire or steering wire 138 used to position thehydrogel deployment feature of the ablation catheter adjacent to thetissue being treated and may permit the physician to manipulate theshape of the distal portion 10 ^(VIII) of the ablation catheter tobetter conform to the tissue being treated. In the embodiment depictedin FIG. 14, the second lumen 136 is adjacent to an inner peripheral wall156 of the distal portion 10 ^(VIII) of the catheter.

FIG. 15 is a fragmentary, cross-sectional view of the distal portion 10^(IX) of an ablation catheter according to a ninth embodiment of thepresent invention. This cross-sectional view is similar to thecross-sectional view of FIG. 13, but depicts a hydrogel deploymentfeature comprising a longitudinally-extending hydrogel slot 158 (compareslot 54 in FIG. 3 and slot 90 in FIG. 8) and a flexible, permeable orsemi-permeable membrane 88 cooperating to deliver the conductivehydrogel 46 to the tissue 28 being treated. In the particularconfiguration depicted in FIG. 15, the protruding conductive hydrogel iscontained within the flexible, permeable or semi-permeable membrane 88;and it is this membrane 88 that makes contact with the surface 142 ofthe tissue 28 being treated. This membrane may be used, for example, tofacilitate hydrogel containment and/or to ensure that the conductivehydrogel 46 protruding from the distal portion of the ablation cathetertakes a desired configuration as explained further below in connectionwith FIGS. 16-19.

FIGS. 16-19 are fragmentary, isometric top views of the distal portion10 ^(X) of an ablation catheter according to a tenth embodiment of thepresent invention. FIG. 16 is a fragmentary, top view of the distalportion of the ablation catheter prior to deployment of the conductivehydrogel. In this figure, an opening 160 is present at the extremedistal end 162 of the distal portion 10 ^(X) of the ablation catheter,and the conductive hydrogel remains within the catheter shaft, behind ashaped, containment membrane 164. In particular, in FIG. 16, theconductive hydrogel 46 has not yet been forced distally in the cathetershaft to “inflate” or “fill” the shaped, containment membrane 164.Although the opening 160 depicted in FIGS. 16-19 is shown as circular,the opening may have a shape other than circular, if desired. Theopening 160 and the containment membrane 164 together comprise thehydrogel deployment feature in the tenth embodiment.

FIGS. 17, 18, and 19 are fragmentary, top views of the distal portion ofan ablation catheter according to a first variant 10 ^(Xa), a secondvariant 10 ^(Xb), and a third variant 10 ^(Xc), respectively, of thetenth embodiment of the present invention. Referring first to FIG. 17,which depicts the first variant 10 ^(Xa) of the tenth embodiment, theconductive hydrogel has been forced longitudinally, distally (i.e., inthe direction of arrow 166) within the catheter shaft and has now filledthe shaped, containment membrane 168. In this variant, the filledmembrane 168 forms a protuberance having a hemispherical configuration.With the conductive hydrogel 46 thus deployed in the containmentmembrane 168 of this configuration, the distal tip of the ablationcatheter may be used to make point or spot ablations 170 or drag burns.In the second variant 10 ^(Xb), which is depicted in FIG. 18, theshaped, containment membrane 172 has a deployed shape that is slightlydifferent from the deployed shape of the containment membrane 168 ofFIG. 17. In particular, in the variant 10 ^(Xb) of FIG. 18, the filledcontainment membrane 172 forms a knoblike protuberance that bulgesslightly more adjacent to the surface 142 of the tissue 28 than does thehemispherical protuberance of FIG. 17. Thus, the ablation catheter withthe containment membrane 172 of FIG. 18 may be used to make somewhatlarger point or spot ablations 170′ than the catheter having thecontainment membrane of 168 FIG. 17.

In FIG. 19, the containment membrane 174 has yet another deployedconfiguration. In this third variant 10 ^(Xc) of the tenth embodiment ofthe present invention, the filled containment membrane 174 forms aprotuberance at the distal end 162 of the ablation catheter in the shapeof a flattened gob that contacts more of the surface 142 of the tissue28 than is contacted using the membrane shapes 168, 172 respectivelydepicted in FIGS. 17 and 18. In all of the variants 10 ^(Xa), 10 ^(Xb),10 ^(Xc) of the tenth embodiment, the protuberance created by the filledcontainment membrane forms a “conformable surface” that contacts thesurface 142 of the tissue 28 to be treated. By adjusting the specificconfiguration of the shaped, containment membrane, the size and shape ofthe resulting lesion may be adjusted. The containment membrane also maybe hoop-shaped when filled with conductive hydrogel. With such ahoop-shaped or hook-shaped containment membrane, it would be possible tovary the radius of curvature of the resulting, filled, containmentmembrane by increasing or decreasing the pressure on the hydrogelfilling the containment membrane. The ultimate membrane design,configuration, or shape is dictated by the intended ultimate use for thevirtual electrode.

FIGS. 20 and 21 depict hydrogel drug delivery catheters. FIG. 20 is afragmentary, cross-sectional view of the distal portion 176 ^(I) of ahydrogel drug delivery catheter according to an eleventh embodiment ofthe present invention; and FIG. 21 is a fragmentary, cross-sectionalview of the distal portion 176 ^(II) of a hydrogel drug deliverycatheter according to a twelfth embodiment of the present invention. Inthese embodiments, a “loaded” conductive hydrogel matrix 178 is depictedin the first lumen 134 at the distal portion of the catheter. Inparticular, a dispensable drug formulation or other beneficial,chemotherapeutic agent 180 is “loaded into” the hydrogel 178 fordelivery to the tissue 28. The dispensable drug or other beneficialagent 180 loaded into the hydrogel 178 may be water soluble and ionic(either positive or negative). For example, ionic botox or ionicpaxitaxol may be loaded into the hydrogel 178. The dispensable drug orother beneficial agent may be used for the treatment of, for example,cardiac arrhythmias. These catheters may, for example, deliver drugsdirectly to an area of the heart that is producing arrhythmias tocontrol or eliminate those arrhythmias. The delivered substance maycause a linear lesion or a spot lesion similar to the lesions that arecaused by the ablative energy (e.g., RF energy) in the embodimentsdepicted in FIGS. 1-19.

In the hydrogel drug delivery catheters of FIGS. 20 and 21, the hydrogeldeployment feature comprises a permeable or semi-permeable membrane 88to contain the loaded conductive hydrogel matrix 178 and to therebyminimize the amount of hydrogel 178 potentially entering the patient'sbloodstream. Although this membrane is not required, when the membraneis present, the dispensable drug or other beneficial agent 180 permeatesthe membrane, whereas the hydrogel 178 remains substantially (if notcompletely) contained inside of the membrane 88.

The embodiment 176 ^(I) of FIG. 20 is similar to the embodiment 10^(VII) of FIGS. 10-14. During use of the catheter depicted in FIG. 20,however, loaded hydrogel 178 is used and a different type of energy isdelivered to that hydrogel via the electrode than is delivered duringuse of the embodiment of FIGS. 10-14. Rather than delivering, forexample, RF energy to the tissue 28 (see ablative energy lines 148 inFIG. 14), direct current emanating from the electrode is delivered tothe tissue. This embodiment thereby actively delivers the ionicchemotherapeutic substance 180 to the tissue 28. The low-intensitydirect current may be used to drive the ionic agent into the tissue by,for example, iontophoresis. FIG. 21 is similar to FIG. 20, but in thetwelfth embodiment 176 ^(II) the hydrogel deployment feature comprises ahydrogel slot 158 and membrane 88, similar to what is depicted in theninth embodiment of FIG. 15.

FIGS. 22-24 depict multi-purpose, multi-electrode hydrogel diagnosticcatheters. FIG. 22 is a fragmentary, top view of the distal portion 182^(I) of a diagnostic catheter according to a thirteenth embodiment ofthe present invention. The distal portion 182 ^(I) comprises a plurality(e.g., 2 to 50) of isolated, conductive hydrogel disks 184 (or“electrodes”) separated by nonconductive hydrogel disks 186. Theconductive hydrogel disks 184 and the nonconductive hydrogel disks 186are adhered together to form the “stack” depicted in, for example, FIG.22.

FIG. 23 is a fragmentary, cross-sectional view taken along line 23-23 ofFIG. 22. FIG. 23 clearly shows that at least one conductive lead 188 isoperatively/electrically connected with each conductive hydrogel disk184. These conductive leads 188, which may be, for example, silver orsilver-chloride coated wires, transmit electrical signals to and fromthe conductive hydrogel disks 184. In this manner, the conductivehydrogel disks may be connected to monitoring equipment outside of thepatient, and the catheters depicted in FIGS. 22-24 may be used asdiagnostic devices to map the endocardial tissue of the heart at variouslocations.

FIG. 24 is a fragmentary, end view (looking distally) of the distalportion 182 ^(II) of a diagnostic catheter according to a fourteenthembodiment of the present invention. In this embodiment, the distalportion of the catheter comprises a curved or C-shaped section 190, andthe stacked conductive hydrogel disks 184′ and nonconductive hydrogeldisks 186′ are present along an active region of the curved section 190of the distal portion 182 ^(II) of the diagnostic catheter. The distalportion of the catheter need not be C-shaped and may be formed into anydesired shape and configured to any desired size required for aparticular application.

The hydrogel diagnostic catheters depicted in FIGS. 22-24 may includeshape memory wires or steering wires like those depicted in, forexample, FIGS. 12-14 to permit a physician to guide and shape the distalportion of the catheter.

As previously mentioned, the hydrogel used to form the conductive andnonconductive hydrogel disks depicted in the embodiments of FIGS. 22-24is substantially unaffected by moisture. Therefore, these diagnosticcatheters can be placed in, for example, the heart for long periods oftime without changing shape. Also, the hydrogel matrix is hydrophilicand, therefore, lubricious, making it easy to move through the patient'svasculature.

Although several embodiments of this invention have been described abovewith a certain degree of particularity, those skilled in the art couldmake numerous alterations to the disclosed embodiments without departingfrom the spirit or scope of this invention. For example, although eachof the treatment and diagnostic catheters is depicted in the figureswith a circular transverse cross section, the present invention does notrequire this circular cross section. An important feature in thisinvention is that hydrogel is used to treat or diagnose tissue. Theconductive hydrogel used in the different embodiments described abovecomprises a desired hydrogel matrix, whether commercially available orspecially designed, and includes additives that result in desiredelectrical and/or chemical properties. For example, the hydrogel matrixmay be adjusted to achieve a desired electrical resistance for theconductive hydrogel to minimize, if desired, heating of the hydrogelitself during ablation. In other words, the hydrogel matrix may beadjusted so that most of the ablative energy is delivered to the tissuerather than merely heating up the conductive hydrogel itself. Further,although the devices depicted and described are all uni-polar and, thus,a dispersive electrode (e.g., a grounding pad) may be placed on thepatient during use of these devices, certain bi-polar devices that usehydrogel virtual electrodes may also fall within the scope of thepresent invention. All directional references (e.g., upper, lower,upward, downward, left, right, leftward, rightward, top, bottom, above,below, vertical, horizontal, clockwise, and counterclockwise) are onlyused for identification purposes to aid the reader's understanding ofthe present invention, and do not create limitations, particularly as tothe position, orientation, or use of the invention. It is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative only and notlimiting. Changes in detail or structure may be made without departingfrom the spirit of the invention as defined in the appended claims.

1. A catheter for treatment of tissue, the catheter comprising at leastone conductive hydrogel virtual electrode adapted to contact the tissueto be treated.
 2. The catheter of claim 1, wherein said at least oneconductive hydrogel virtual electrode comprises viscoelastic hydrogel.3. The catheter of claim 1, wherein said at least one conductivehydrogel virtual electrode comprises conductive, hemocompatiblehydrogel.
 4. The catheter of claim 1, wherein said hydrogel isradiopaque.
 5. The catheter of claim 1, wherein said catheter has adistal portion comprising a straight section; a hoop-shaped section; anoffset that joins said straight section to said hoop-shaped section; anactive region along said hoop-shaped section; and a hydrogel deliveryfeature along said active region, wherein said hydrogel delivery featureis adapted to be placed against the tissue to be treated.
 6. Thecatheter of claim 5, wherein said hoop-shaped section defines adistally-facing surface, wherein said hydrogel delivery feature is onsaid distally-facing surface, and wherein said hydrogel delivery featurecomprises an opening selected from the group consisting of a single rowof hydrogel portholes, a plurality of rows of hydrogel portholes, asingle hydrogel slot, and a plurality of hydrogel slots.
 7. The catheterof claim 5, wherein said hoop-shaped section defines a distally-facingsurface, wherein said hydrogel delivery feature is on saiddistally-facing surface, wherein said distally-facing surface defines adistally-facing radial apex, and wherein said hydrogel delivery featureis symmetrically located about said distally-facing radial apex.
 8. Thecatheter of claim 7, wherein said hydrogel delivery feature comprises aplurality of distally-facing hydrogel portholes arranged in a single rowalong a porthole centerline, and wherein said distally-facing radialapex defines a C-shaped line coincident with said porthole centerline.9. The catheter of claim 7, wherein said distally-facing radial apexdefines a C-shaped line, and wherein said hydrogel delivery featurecomprises concentric arcs of hydrogel portholes including a firstplurality of hydrogel portholes along an outer arc and a secondplurality of hydrogel portholes along an inner arc.
 10. The catheter ofclaim 9, wherein said hydrogel portholes of said first plurality ofhydrogel portholes along said outer arc are staggered across saidC-shaped line from corresponding hydrogel portholes of said secondplurality of hydrogel portholes along said inner arc, the firstplurality and the second plurality of hydrogel portholes togetherforming a zigzagging row of hydrogel portholes.
 11. The catheter ofclaim 7, wherein said hydrogel delivery feature comprises alongitudinally-extending hydrogel slot that straddles a slot centerline,and wherein said distally-facing radial apex defines a C-shaped linecoincident with said slot centerline.
 12. The catheter of claim 7,wherein said hydrogel delivery feature comprises a plurality oftransversely-extending hydrogel slots spaced along a slot centerline,and wherein said distally-facing radial apex defines a C-shaped linecoincident with said slot centerline.
 13. The catheter of claim 5,wherein said hoop-shaped section defines a radially outer peripheralwall, wherein said outer peripheral wall defines an outwardly-facingsurface, wherein said hydrogel delivery feature is on saidoutwardly-facing surface, wherein said hydrogel delivery featurecomprises at least one opening extending through said outer peripheralwall and said outwardly-facing surface, wherein said at least oneopening extends through said outer peripheral wall radially relative toa center of an imaginary circle tracing said hoop-shaped section, andwherein said at least one opening is selected from the group consistingof a single row of hydrogel portholes, a plurality of rows of hydrogelportholes radially, a single hydrogel slot, and a plurality of hydrogelslots.
 14. The catheter of claim 5, wherein said hoop-shaped sectiondefines a radially outer peripheral wall, wherein said outer peripheralwall defines an outwardly-facing surface, wherein said hydrogel deliveryfeature is on said outwardly-facing surface, wherein saidoutwardly-facing surface defines an outwardly-facing radial apex, andwherein said hydrogel delivery feature is symmetrically located aboutsaid outwardly-facing radial apex.
 15. The catheter of claim 14, whereinsaid hydrogel delivery feature comprises a plurality of outwardly-facinghydrogel portholes arranged in a single row along a porthole centerline,and wherein said outwardly-facing radial apex defines a C-shaped linecoincident with said porthole centerline.
 16. The catheter of claim 14,wherein said outwardly-facing radial apex defines a C-shaped line, andwherein said hydrogel delivery feature comprises side-by-side arcs ofhydrogel portholes including a first plurality of hydrogel portholesalong a distal arc and a second plurality of hydrogel portholes along aproximal arc.
 17. The catheter of claim 16, wherein said hydrogelportholes of said first plurality of hydrogel portholes along saiddistal arc are stationed symmetrically across said C-shaped line fromcorresponding hydrogel portholes of said second plurality of hydrogelportholes along said proximal arc, each hydrogel porthole of said distalarc having a corresponding hydrogel porthole along said proximal arc.18. The catheter of claim 14, wherein said hydrogel delivery featurecomprises a longitudinally-extending hydrogel slot that straddles a slotcenterline, and wherein said outwardly-facing radial apex defines aC-shaped line coincident with said slot centerline.
 19. The catheter ofclaim 14, wherein said hydrogel delivery feature comprises a pluralityof transversely-extending hydrogel slots spaced along a slot centerline,and wherein said outwardly-facing radial apex defines a C-shaped linecoincident with said slot centerline.
 20. The catheter of claim 1,wherein said catheter has a distal portion comprising a straight activeregion, said straight active region extending parallel to a catheterlongitudinal axis; and a hydrogel delivery feature along said straightactive region, said hydrogel delivery feature being adapted to be placedagainst the tissue to be treated.
 21. The catheter of claim 20, whereinsaid straight active region defines an outer peripheral wall, whereinsaid outer peripheral wall defines an outwardly-facing surface, whereinsaid hydrogel delivery feature is on said outwardly-facing surface, andwherein said hydrogel delivery feature is selected from the groupconsisting of a single row of hydrogel portholes extending through saidouter peripheral wall toward and along said catheter longitudinal axis,a plurality of rows of hydrogel portholes extending through said outerperipheral wall toward and along said catheter longitudinal axis, asingle hydrogel slot extending through said outer peripheral wall towardand along said catheter longitudinal axis, and a plurality of hydrogelslots extending through said outer peripheral wall toward and along saidcatheter longitudinal axis.
 22. The catheter of claim 20, wherein saidstraight active region defines an outer peripheral wall, wherein saidouter peripheral wall defines an outwardly-facing surface, wherein saidhydrogel delivery feature is on said outwardly-facing surface, whereinsaid outwardly-facing surface defines an outwardly-facing radial apex,and wherein said hydrogel delivery feature is symmetrically locatedabout said outwardly-facing radial apex.
 23. The catheter of claim 22,wherein said hydrogel delivery feature comprises a plurality ofoutwardly-facing hydrogel portholes arranged in a single row along aporthole centerline, and wherein said outwardly-facing radial apexdefines a straight line coincident with said porthole centerline. 24.The catheter of claim 22, wherein said hydrogel delivery featurecomprises a longitudinally-extending hydrogel slot that straddles a slotcenterline, and wherein said outwardly-facing radial apex defines astraight line coincident with said slot centerline.
 25. The catheter ofclaim 1, wherein said catheter shaft comprises a first lumen adapted tocontain a displaceable segment of said conductive hydrogel used to formsaid at least one hydrogel virtual electrode.
 26. The catheter of claim25, wherein said first lumen comprises a nearly-circular subportion anda rounded-rectangular subportion, and wherein said rounded-rectangularsubportion retains an electrode adapted to deliver ablative energythrough said at least one conductive hydrogel virtual electrode to thetissue being treated.
 27. The catheter of claim 25, wherein saidcatheter shaft further comprises a second lumen adapted to contain asteering wire to position said at least one conductive hydrogel virtualelectrode against the tissue being treated.
 28. A catheter for treatmentof tissue, the catheter comprising at least one conductive hydrogelvirtual electrode, wherein said at least one conductive hydrogel virtualelectrode is contained within a containment membrane adapted to contactthe tissue to be treated.
 29. The catheter of claim 28, wherein saidmembrane is selected from the group consisting of permeable andsemi-permeable membranes.
 30. The catheter of claim 28, wherein saidmembrane comprises a shaped membrane adapted to take a predeterminedconfiguration when filled with conductive hydrogel.
 31. The catheter ofclaim 30, wherein said catheter has a distal portion comprising ahydrogel delivery feature comprising an opening adapted to be placedadjacent to the tissue to be treated; and said containment membrane,wherein said containment membrane is secured at said opening, andwherein said containment membrane, when filled with conductive hydrogel,is adapted to form a protuberance having a conformable surface tocontact the tissue to be treated.
 32. The catheter of claim 31, whereinsaid protuberance is selected from the group consisting of a hemisphere,a knob, a flattened gob, a hook, and a hoop.
 33. A drug deliverycatheter for treatment of cardiac arrhythmias, the catheter comprising adistal portion comprising an active region; a lumen extending insidesaid catheter adjacent to said active region; and a hydrogel deliveryfeature along said active region and in fluid communication with saidlumen, wherein said hydrogel delivery feature is adapted to be placedagainst arrhythmia-producing, cardiac tissue inside of a heart; and aconductive hydrogel matrix in said lumen, wherein said conductivehydrogel matrix is loaded with a water-soluble and ionic dispensabledrug formulation.
 34. The drug delivery catheter of claim 33, whereinsaid hydrogel delivery feature comprises a plurality of hydrogelportholes; and a permeable membrane attached at said plurality ofhydrogel portholes and adapted to be alternatingly extendable out of andretractable back into said plurality of hydrogel portholes, wherein saidmembrane is adapted to contain said conductive hydrogel matrix, whereinsaid membrane is adapted to make contact with the cardiac tissue, andwherein said membrane is adapted to be traversable by said drugformulation.
 35. A drug delivery system for treatment of cardiacarrhythmias, the system comprising a catheter having a distal portioncomprising an active region; a lumen extending adjacent to said activeregion, said lumen being adapted to contain a conductive hydrogel matrixloaded with a water-soluble and ionic dispensable drug formulation; anda hydrogel delivery feature comprising an opening through said activeregion, said opening being in fluid communication with said lumen andbeing adapted to be placed against arrhythmia-producing, cardiac tissue;and a permeable membrane attached at said opening and adapted to bealternatingly extendable out of and retractable back into said opening,wherein said membrane is adapted to contain the conductive hydrogelmatrix, wherein said membrane is adapted to make contact with thecardiac tissue, and wherein said membrane is adapted to be traversableby the ionic dispensable drug formulation; and a current supply adaptedto deliver low-intensity direct current to the conductive hydrogelmatrix.
 36. The drug delivery system of claim 35, wherein said openingthrough said sidewall of said catheter is selected from the groupconsisting of at least one hydrogel porthole and at least one hydrogelslot.
 37. A diagnostic catheter for diagnosing cardiac tissue, thecatheter comprising at least one conductive hydrogel sensing electrode.38. The diagnostic catheter of claim 37, wherein said at least oneconductive hydrogel sensing electrode comprises a plurality of isolated,conductive hydrogel disks that are electrically separated bynonconductive hydrogel disks, and wherein said conductive andnonconductive hydrogel disks are constructed from high-viscosity, rigidhydrogel that is substantially unaffected by moisture.
 39. Thediagnostic catheter of claim 38, wherein said conductive hydrogel disksare adhered to said nonconductive hydrogel disks.
 40. The diagnosticcatheter of claim 38, wherein each of said plurality of conductivehydrogel disks is electrically connected with a separate electricallead.
 41. The diagnostic catheter of claim 40, wherein each of saidseparate electrical leads comprises a silver or silver-chloride coatedwire.
 42. A method of treating cardiac tissue, the method comprising thesteps of guiding an ablation catheter having at least one conductivehydrogel virtual electrode to the cardiac tissue to be treated;introducing said at least one conductive hydrogel virtual electrodeagainst the cardiac tissue; and directing ablative energy to the cardiactissue via said at least one conductive hydrogel virtual electrode. 43.A method of treating cardiac tissue, the method comprising the steps offilling at least a distal portion of a catheter lumen with conductivehydrogel, said catheter lumen extending adjacent to a catheter activeregion on a catheter outer surface; guiding said catheter active regioninto contact with the cardiac tissue to be treated; activating ahydrogel displacement device to advance said conductive hydrogel towardsaid active region until said conductive hydrogel broaches said catheterouter surface to thereby introduce at least one conductive hydrogelvirtual electrode against the cardiac tissue; directing ablative energythrough said at least one conductive hydrogel virtual electrode and intothe cardiac tissue; and activating said hydrogel displacement device toretract said conductive hydrogel and thus said at least one conductivehydrogel virtual electrode from contact with the cardiac tissue and backinto said catheter lumen.
 44. The method of claim 43, wherein saidactivating steps further comprise activating a pump to move saidconductive hydrogel distally and proximally within said catheter lumen.